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CHAPTER 1
INTRODUCTION
1.1
Overview
The dawn of the 20th century, marked the beginning of the use of
haloaliphatic compounds in industries and agriculture. After some decades of
their discovery, the hazard associated with the use of these compounds started to
manifest in the environment and in living organisms. The quest by people for a
cleaner lifestyle lead to the use of man-made chemical such as haloaliphatic
hydrocarbon compounds as herbicide, pesticide, fungicides, paint, solvents and
industrial chemicals which cause harmful damage to the environment via a
pollution (Rasul and Chapalamaduqu, 1991).
Halogenated compounds are very essential group of xenobiotics. 3chloropropionic acid (3CP) that belongs to the class of chlorinated mono
carboxylic acid or β-chloro substituted haloalkanotes. They are considered as a
possible chemical inclusion in pesticides. This compound has a carcinogenic and
genotoxic effect on animals and humans (Jing and Huyop, 2007).
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A major process through which xenobiotic chemicals such as
chloroaliphatic compounds is removed from the environment by microorganisms
is called biodegradation (Sinha et al., 2009). The microbial degradation of a
contaminant usually occurs because microorganisms derive support for growth
through the use of the contaminant as an electron donor and carbon source.
Hydrolytic dehalogenases typifies the major step in the degradation of
haloaliphatic compounds. These enzymes propel the cleavage of halogen-carbon
bonds by nucleophilic substitution, and change the halogen ion by a hydroxyl
group obtained from water (Schwarze et al., 1996). Field and Alvarez (2004 )
noted that by using the dehalogenase enzyme, compounds containing chlorine are
being metabolized and chlorine substituent are enzymatically removed to form
non-halogenated compounds.
The decontamination of these substances can be done by using biological
or non-biological degradation process. Since the biological methods are
reasonable, harmless, and environmentally friendly, they are favored (Janssen et
al., 2005). Bioremediation is a process that involves the use of biological
methods like microbial or enzymatic biocatalysts (Janssen et al., 2001). Many
years ago, studies on microbial degradation of harmful waste started, due to
growing of xenobiotic compounds in industrial and agricultural uses. Microbial
degradation of xenobiotic chemicals such as chloroaliphatic compounds involves
the ways and processes of biodegradation that assist in removing these
compounds from the environment. There are so many studies had been done on
the microbial catabolism of dehalogenase (Olaniran et al., 2001, 2004; Jing and
Huyop, 2007; Jing et al., 2008). Most of the degradation pathway of halogenated
compounds includes dehalogenation, the cleavage of the carbon-halogen bond to
release halogen, catalyzed by 'dehalogenase' (Fetzner and Lingens, 1994; Janssen
et al., 2005).
The ability of the enzyme to catalyze the dehalogenation of various
halogen-substituted organic acids was investigated and the highest activity was
found with 3-chloropropionic acid as a sole carbon source in the growth medium
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(Jing et al,.2008). There are many different microorganisms (like bacteria and
fungi) which are capable of utilizing halogenated compound as the only carbon
source and consequently, are supposed to have a significant role in their natural
detoxification (Janssen et al., 2001; Song et al., 2003; Park et al., 2003), and is a
major step in aerobic mineralization pathways of many halogenated compounds
that occur as environmental pollutants (Janssen et al., 2005). A number of these
microorganisms were originally isolated from polluted soil and sewage oxidation
ponds (Olaniran et al., 2001, 2004). So far, fungi had been found to be isolated to
degrade halogenated compound particle (α-haloalkanoic acid).
The current study focuses on the isolation and identification of other
environmental microorganisms to dissociate the presence of 3-chloropropionic
acid. In detail, the aim of this study is identification of the fungus isolated from
the bread that can degrade 3-chloropropionic acid based on the 18S rRNA
molecular approach. This will be a genotypic dependable approach to
characterize the isolated fungi, compared to conventional methods like
morphological procedures.
1.2
Problem statement
The widespread usage of chloroaliphatic hydrocarbon compounds in industries has
resulted in extensive pollution of environment and the ground water (Fliermans,
1989). Chlorinated aliphatic compounds form one of the most vital groups of
industrially produced chemicals. Several of these compounds are weakly degraded in
the environment (Reineke, 2001). The 3-chloropropionic acid which is one of these
compounds, considered as a possible chemical inclusion in certain herbicide and
carcinogenic and genotoxic to the animal and human. The uses of herbicides in
general (2,2DCP and 3CP) are the main contributor of the environmental pollution
(Jing et al., 2005). Aerobic biodegradation by using microorganisms such as fungi, to
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degrade the chloroaliphatic hydrocarbon compounds to carbon dioxide, water, and
hydrogen chloride is more efficient than anaerobic or chemical processes. Therefore,
the aerobic biodegradation by using microorganism such as fungi is preferable as it is
costly and biologically effective.
1.3
Goals and Objectives
The main goals of the current research were to isolate and identify 3chloropropionic acid degrading fungi. Therefore, to achieve these goals, the
following objectives were considered:
(i)
To isolate of a single fungus from the Bread that can degrade 3CP.
(ii)
To identify and characterize the isolated fungus by determining the
morphological appearances and genetic sequence analysis.
(iii)
To study the growth capability of isolated fungus on 3CP.
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1.4
Research Scope
The scope of this research includes the molecular identification of the
fungus that isolated from bread, which has ability to degrade 3-chloropropionic
acid by amplifying the ITS region, whereas the universal ITS primers (ITS1 and
ITS4) used to run the PCR (White et al., 1990). In addition, the conventional
methods that used for further identification and characterization.
1.5
Research Significance
The outcome of this study tends to identify fungal species from bread
capable of degrading 3CP compounds. Novel fungal species was isolated, which
has the ability of degrading the chloroaliphatic compounds and this new strain of
fungus, which is previously unknown for its reaction of chloroaliphatic
compounds.